See also the official documentation:
Help Center > Group Owners Manual > Exporting or downloading your group's data > Downloading your group's member list

In Admin, Members, click on Download at the top of the page.

The list you see is a CSV file of the information.  You should be able to use your browser to Save Page As (or similar), then you can use a spreadsheet to sort it out.

- Save Page or Save as (or whatever your browser calls it) and you're done.
 
- If you have several groups, rename it to [groupname].csv before saving. 

In Chrome, you can right-click on the page and select Save As...

In Edge, right-click, Select-All, open Notepad, paste, save as members.csv (or whatever name you like with .csv extension)

In Safari, save as Page Source.

In Firefox (Apple version), save Plain Text Document.

- Open your saved document with spreadsheet software, such as Excel, Numbers (Apple), Google Sheets.